1. Field of the Invention
This invention relates to lead free machinable copper based alloys and, in particular, to an additive comprising bismuth selenide for making machinable copper based alloys such as brasses which alloys can be substituted for conventional lead containing brasses in potable water applications.
2. Description of Related Art
Copper based alloys are used in many products and applications. Potable water products, such as plumbing fixtures and piping, use brasses and other copper based alloys. Lead, in amounts of about 1-9%, has been employed as an alloying ingredient in brasses to improve the machinability of the alloy. Red brasses contain about 2 to 8% zinc or more and are resistant to stress corrosion cracking and are easily formed. Yellow brasses contain greater than about 17% zinc, e.g., 30-45% zinc and have good ductility and high strength and can withstand cold working. Each type brass is preferred for certain applications.
Ingestion of lead by humans is considered harmful however, and the use of lead is being severely curtailed due to health and environmental concerns. Drinking water is one such concern and legislation has been proposed to reduce the concentration of lead in plumbing fixtures and fittings and thus to reduce the amount of lead leached into the water. Accordingly, there have been attempts to reduce the lead content of alloys and numerous elements have been proposed as substitutes for lead. The term "lead free" alloys referred to herein means that the alloy contains less lead than it usually contains and preferably less than 2%.
The substitutes for lead must also meet workplace, health and environmental standards and while there are substitutes for lead these materials present their own problems when used to make the alloy and in their fabrication and use of the alloy. Many of the materials are difficult to alloy and react violently when added to copper based alloys in the alloy making process and fume excessively causing safety, health and environmental problems. Likewise, some materials tend to leach from the alloy during use and cannot therefore be used in potable water applications.
Bismuth is considered non-toxic and has been used as a substitute for lead to improve the machinability of alloys. A number of patents have issued showing alloys having reduced lead contents with bismuth as a substitute.
U.S. Pat. No. 4,879,094 discloses a cast copper alloy containing 1.5-7% bismuth, 5-15% zinc, 1-12% tin and the balance copper. Another free machining brass is disclosed in Japanese Application 54-135618 containing 0.5-1.5% bismuth, 58-65% copper and the balance zinc. U.S. Pat. No. 5,360,591 shows reduced lead yellow brasses for plumbing applications containing 0-1% lead, 0.2-1.5 aluminum, 0.2-1.5% bismuth, 30-45% zinc and 55-70% copper. Japanese Applications 57-73149 and 57-73150 disclose copper alloys containing bismuth and additions of graphite and titanium and manganese. U.S. Pat. No. 5,167,726 discloses a wrought copper alloy containing bismuth and phosphorous, tin or indium. U.S. Pat. No. 5,137,685 discloses a copper alloy in which the lead content is reduced by the addition of bismuth. The alloy contains 30-58% zinc. To improve its machinability a sulfide, telluride or selenide may be added to the alloy or, to enhance their formation an element which combines with them such as zirconium, manganese, magnesium, iron, nickel or mischmetal may be added.
Selenium is likewise known for use in copper base alloys and additions of 0.25-1% as copper selenide improve the machinability of the alloy more than do sulfur, tellurium or bismuth and have little effect on the strength and decreases the ductility and conductivity only slightly. Studies of the microstructure of selenium containing copper shows the presence of Cu--Cu.sub.2 Se eutectic which serves to break up the chips during machining.
Selenium however, unlike bismuth, is considered toxic and is controlled by regulations limiting the amount of selenium in the workplace and in the environment. Selenium when added to a copper base alloy in the alloy making process fumes excessively and poses a health hazard. The use of selenium therefore, while useful as a substitute for lead, suffers from many of the same problems as lead.
Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide lead free copper based alloys made by adding bismuth selenide to the alloy as a substitute for lead, the alloys being machinable and suitable for uses in which there are manufacturing, health and environmental concerns.
It is another object of the present invention to provide lead free brasses which are machinable and which may be used in potable water applications.
A further object of the invention is to provide an environmental and safe method for making lead free copper base alloys including lead free brasses which contain bismuth and selenium added as bismuth selenide as a substitute for lead and which are machinable and may be used in potable water applications.
It is yet another object of the present invention to provide an additive product comprising bismuth selenide for making copper base alloys including brasses.
An additional object of the invention is to provide a method for making a additive comprising bismuth selenide which additive can be used to make lead free alloys including copper based alloys and brasses.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.